1. Field of the invention
The invention relates to an apparatus and method for identifying a misfiring cylinder(s) in a multiple cylinder internal combustion engine.
2. Description of the Related Art
When misfiring occurs in a multiple cylinder internal combustion engine, not only is there a fluctuation in torque but the fuel supplied to the cylinder that is misfiring is discharged as it is, which adversely affects exhaust emissions. Therefore, when there is a misfire, the supply of fuel to the cylinder that is misfiring is stopped in an attempt to prevent emissions from becoming worse. In order to halt the misfiring cylinder, however, it is necessary to identify which cylinder is misfiring.
A misfiring cylinder is typically identified by counting the number of times the revolution speed fluctuation amount exceeds a specified misfire determining value and specifying the cylinder with greatest number of times counted as the misfiring cylinder, as is described in Japanese Patent Application Publication No. 5-18311 (JP-A-5-18311), for example. This method can be effective for identifying a misfiring cylinder when a single cylinder is misfiring.
However, when a plurality of cylinders misfires simultaneously, it is difficult to effectively identify the misfiring cylinders using that method alone. Therefore, a misfiring cylinder identifying apparatus that can identify a misfiring cylinder(s) even when a plurality of cylinders misfires simultaneously has been proposed in Japanese Patent Application Publication No. 2003-343340 (JP-A-2003-343340) or Japanese Patent Application Publication No. 10-318033 (JP-A-10-318033). For example, the apparatus described in JP-A-2003-343340 identifies the misfiring cylinder(s) by determining whether a single cylinder is misfiring, two consecutive cylinders are misfiring, or two intermittent cylinders are misfiring from the revolution speed fluctuation pattern. Also, the apparatus described in JP-A-10-318033 identifies the misfiring cylinder(s) by determining whether a single cylinder is misfiring, two consecutive cylinders are misfiring, or two intermittent cylinders are misfiring from the revolution speed fluctuation pattern of three consecutive cylinders in the firing order.
When identifying a misfiring cylinder based on the revolution speed fluctuation pattern as described in the related art in an internal combustion engine with a small number of cylinders, such as six or less for example, the misfiring cylinder(s) can be appropriately identified. However, it becomes more difficult to appropriately identify the misfiring cylinder(s) with the related art described above as the number of cylinders increases. This is because the number of possible misfiring cylinder combinations increases exponentially as the number of cylinders increases. For example, when no more than two cylinders misfire simultaneously, the possible misfiring cylinder combinations is 10 in a four-cylinder internal combustion engine, 21 in a six-cylinder internal combustion engine, and 36 in an eight-cylinder internal combustion engine. Moreover, the number of possible misfiring cylinder combinations increases even more when three or more cylinders misfire simultaneously.
In order to identify a misfiring cylinder(s) based on revolution speed fluctuation pattern matching as in the related art described above, it is necessary to obtain the revolution speed fluctuation pattern for each possible misfiring cylinder combination beforehand, and reference all of the obtained revolution speed fluctuation patterns. Therefore, as the number of cylinders increases, so too does the number of revolution speed fluctuation patterns that must be obtained beforehand, and the misfiring cylinder identifying logic becomes complicated. Accordingly, in an internal combustion engine with a large number of cylinders it is difficult to identify misfiring cylinders based only on revolution speed fluctuation pattern matching as in the related art described above.